1. Field of the Invention
The present invention relates to a cathode ray tube such as a color picture tube and a color monitor, and in particular to an improved cathode ray tube which can prevent an interference from taking place to an electron beam deflection trajectory, by sufficiently obtaining the atmospheric pressure resistance of a vacuum vessel, and margin of a beam shadow neck BSN which causes a problem when adjusting a deflection yoke.
2. Description of the Background Art
FIGS. 1 and 2 illustrate an example of a conventional cathode ray tube, respectively. FIG. 1 is a side-sectional view illustrating a color picture tube, and FIG. 2 is a front view illustrating a fluorescent screen provided in a panel.
As shown therein, the cathode ray tube which has been generally known as a Braun tube includes a vacuum vessel 10 having: a glass panel 3 consisting of an image receiving unit 1 similar to a rectangle having a tube axis Z, a horizontal axis X and a vertical axis Y, and a skirt portion 2 provided around the image receiving unit 1; a glass funnel 4 firmly connected to the skirt portion 2, for maintaining a vacuum state in the cathode ray tube; and a cylindrical glass neck 7 connected to an end portion of the glass funnel 4 having a smaller diameter.
A fluorescent screen 5 having dot- or stripe-shaped fluorescent layers of three colors, blue, green and red is disposed at the panel 3.
An electron gun 9 emitting three electron beams 8 is provided in the neck 7. The electron gun 9 is an in-line type electron gun emitting the three electron beams 8 arranged in a line on an identical horizontal surface.
In addition, a yoke mounting portion 11 is disposed at a predetermined portion between the neck 7 and funnel 4 of the vacuum vessel 10. A deflection yoke 6 deflecting the electron beam 8 emitted from the electron gun 9 to the whole screen is mounted on the yoke mounting portion 11, thereby generating a pincushion type horizontal deflection magnetic field and a barrel type vertical deflection magnetic field.
The electron beam 8 emitted from the electron gun 9 is deflected in a horizontal deflection direction X and a vertical deflection direction Y generated by the deflection yoke 6. Accordingly, when reaching to the fluorescent screen 5 through a shadow mask (not shown) distinguishing colors, the three electron beams arranged in a line are concentrated on the whole fluorescent screen 5 without requiring a specific compensating device, and color images are displayed by horizontal and vertical scanning.
The above-described color picture tube is a line type color picture tube of self convergence, and widely practically used.
It is very important to reduce consumption power of the deflection yoke 6 which is a maximum power consumption source in the cathode ray tube such as the color picture tube.
That is to say, it is necessary to increase an anode voltage which finally accelerates the electron beam in order to improve screen luminance, and it is also necessary to increase a deflection frequency so as to correspond to office automation OA apparatuses including a high definition television HDTV and a personal computer PC, which increases deflection power, namely the consumption power of the deflection yoke 6.
Especially when the electron beam is deflected by a high frequency, the deflection magnetic field may be easily externally leaked from the cathode ray tube. Accordingly, restrictions are enhanced in regard to the leakage magnetic field of the cathode ray tube, namely the OA apparatuses such as the personal computer.
In the deflection yoke 6, a method of using a compensating coil as a means for reducing the magnetic field leaked from the cathode ray tube has been generally employed.
However, to use the compensating coil increases the consumption power of the personal computer.
In general, when reducing the deflection power or leakage magnetic field, it is preferable to efficiently operate the deflection magnetic field in regard to the electron beams, by decreasing a diameter of the neck 7 of the cathode ray tube, an outer diameter of the yoke mounting portion 11 on which the deflection yoke 6 is mounted, and an operational space of the deflection magnetic field.
In the above-described cathode ray tube, in case the electron beam 8 is deflected in a direction of a maximum diameter of the screen, namely a diagonal direction, a deflection angle of the electron beam, namely an angle between the tube axis Z and the deflected electron beam 8 is increased.
When the deflection angle of the electron beam 8 is increased, the electron beam 8 passes near the yoke mounting portion 11 of the funnel on which the deflection yoke 6 is mounted.
Accordingly, when the diameter of the neck 7 or the outer diameter of the yoke mounting portion 11 of the funnel 4 is simply decreased, as illustrated in FIG. 1, the outer-side electron beam 8 collides with an inner wall P1 near the neck 7 of the funnel 4. In addition, as illustrated in FIG. 2, a region of the fluorescent screen 5 where the electron beam 8 does not reach, namely a non-luminescence portion P2 is generated.
Therefore, in the conventional cathode ray tube, it is impossible to simply decrease the diameter of the neck 7 or the outer diameter of the yoke mounting portion 11 of the funnel 4. As a result, it is difficult to reduce the deflection power or leakage magnetic filed.
In order to overcome the above-described disadvantage, it is disclosed in Japanese Patent Application 48-34349 a vacuum vessel 20 of the cathode ray tube having a different shape as depicted in FIGS. 3 to 5, based on the fact that a passing region defined according to a trajectory of the electron beam 8 passing the yoke mounting portion 11 near the neck 7 of the funnel 4 forms a shape similar to a rectangle, in the case of drawing a rectangular raster on the fluorescent screen 5.
In the vacuum vessel 20, as shown in FIGS. 4A to 4E taken along lines Bxe2x80x94B to Fxe2x80x94F, respectively, the sectional shape from the neck 7 of the funnel 4 where the deflection yoke 6 is mounted to the funnel 4 is varied from a round shape to a shape similar to the rectangle via an elliptical shape.
As compared with the vacuum vessel of the cathode ray tube having the round-shaped yoke mounting portion 11 near the neck 7 of the funnel 4, the vacuum vessel 20 has a shape similar to the rectangle.
Accordingly, the horizontal deflection coil and the vertical deflection coil of the deflection yoke are positioned at the passing region of the electron beam 8, and thus the electron beam 8 is efficiently deflected, thereby reducing the deflection power.
However, in the conventional vacuum vessel 20, the sectional shape of the side of the neck 7 of the funnel 4 where the deflection yoke 6 is mounted, namely the sectional shape of the yoke mounting portion 11 forms a shape similar to the rectangle, and accordingly the strength of the inside air pressure is decreased, thereby reducing stability. Thus, it is difficult to sufficiently reduce the deflection power.
On the other hand, in general, the more the deflection angle of the electron beam 8 is increased, the more a length of a tube of the cathode ray tube, namely a length of the whole neck 7 is shortened.
For instance, a deflection tube of 110xc2x0 has been developed by utilizing enlarged angle deflection. However, in the case that the enlarged angle deflection is simply performed, the deflection angle of a diagonal portion is increased, thereby causing a beam shadow neck BSN.
According to Japanese Patent Application 58-225545, the beam shadow neck BSN is overcome by providing a groove at the diagonal portion in a cone-shaped portion of the funnel.
As described above, in the conventional cathode ray tube, the deflection yoke is designed according to the funnel. However, in a pyramid-shaped funnel and deflection yoke structure, when designing the side of the neck of the funnel, namely the yoke mounting portion, an optimal inside shape is set by considering the trajectory of the electron beam, an explosion proof property and the beam shadow neck BSN. There is a restriction of designing the funnel according to the deflection yoke, as in the order of designing the deflection yokexe2x86x92modeling the shape of the deflection yokexe2x86x92computing the magnetic fieldxe2x86x92analyzing the trajectory of the electron beamxe2x86x92analyzing stress of a funnel bulbxe2x86x92re-designing the deflection yoke. Thus, in a state where a funnel inside numeral is almost set, it is required the optimization of the funnel outside design for improving the strength of the inside air pressure by considering the deflection sensitivity and the explosion proof property.
However, in the conventional cathode ray tube, when the inside shape of the yoke mounting portion where the beam shadow neck BSN is generated is formed according to a deflection center point, it has a constant curvature so long as there is no inflection point.
In the case of the enlarged angle deflection having the shape of the yoke deposition portion of the funnel as described above, when the deflection yoke is adjusted, a slant of the deflection angle of the electron beam is sharply varied, thereby causing the beam shadow neck BSN generating shadow on the screen.
In addition, in order to prevent the beam shadow neck BSN, as disclosed in Japanese Patent Application 58-225545, in the case that a thickness difference of long and short sides and a diagonal portion is excessively set, a maximum vacuum strength (tension strength) is increased at the funnel diagonal portion, and thus explosion may occur during an exhaust process. Besides, a distance between the deflection coil and the electron beam passing region is increased, and accordingly the deflection power is increased. On the other hand, when a thickness ratio of the diagonal portion and the long and short sides is sufficiently set for the explosion proof and the reduction of the deflection consumption power, the beam shadow neck BSN may be generated, thereby weakening strength of the long and short sides.
Especially, in the conventional cathode ray tube, since the beam shadow neck BSN is mostly generated from the deflection center line to the funnel inside diagonal portion, it is difficult to avoid the neck shadow. In addition, there is little margin of the rotation of the deflection yoke in the ITC works (optimizing the screen by adjusting the deflection yoke when mounting the deflection yoke after fabricating the tube). As a result, productivity thereof is reduced.
Accordingly, it is a primary object of the present invention to provide a cathode ray tube which can sufficiently obtain strength of an inside air pressure of a vacuum vessel, restrict generation of a beam shadow neck BSN by a constant curvature of a yoke mounting portion, and reduce deflection power of a deflection yoke.
It is another object of the present invention to provide a cathode ray tube which can improve deflection sensitivity, by positioning an inner surface of a yoke mounting portion near a trajectory of an electron beam, and forming a predetermined inflection point at the yoke mounting portion.
It is still another object of the present invention to provide a cathode ray tube which can prevent an interference from occurring in regard to a beam deflection trajectory and sufficiently obtain strength of an inside air pressure, when forming a predetermined inflection point at an inner surface of a funnel, and adjusting a deflection yoke.
In order to achieve the above-described objects of the present invention, there is provided a cathode ray tube including: a vacuum envelope having a face panel including a substantially rectangular effective portion having horizontal and vertical axes which cross at right angles and pass a tube axis, a funnel connected to the face panel, a neck connected to a smaller-diameter end of the funnel, and a phosphor screen formed on an inner surface of the effective portion of the face panel, the funnel including a yoke attachment portion extending from the smaller-diameter end connected to the neck toward the face panel; an electron gun arranged within the neck, for emitting an electron beam to the phosphor screen; and a deflection yoke mounted on outer surfaces of the neck and the yoke attachment portion of the funnel, for deflecting the electron beam emitted from the electron gun along the horizontal and vertical axes so as to cause the electron beam to scan the phosphor screen; at least one cross section of the yoke attachment portion, perpendicular to the tube axis, having a substantially rectangular outer contour which includes a pair of first opposed sides that traverse the horizontal axis, and a pair of second opposed sides that traverse the vertical axis, and a substantially rectangular inner contour which includes four corner sides defined by a concave shape toward the tube axis.
In order to achieve the above-described objects of the present invention, there is provided a cathode ray tube wherein an inner surface of a diagonal portion of a yoke mounting portion is inflected in a normal direction, having a predetermined depth and width, when a recession depth is S and a funnel thickness is T, the recession depth of the yoke mounting portion being at the range of 0.1xc3x97Tmmxe2x89xa6Sxe2x89xa60.5xc3x97Tmm, when a recession width is W, the recession width of the yoke mounting portion being at the range of 0.5 mmxe2x89xa6Wxe2x89xa615.0 mm, and when a deflection center line of an electron gun is R, and a position of an inflection point of the funnel on a tube axis is L, the position of the inflection point being at the range of R+0.5 mmxe2x89xa6Lxe2x89xa6R+20 mm.